This invention relates to an apparatus for chemically treating a metal part including but not limited to phosphate and other conversion coatings which are applied to the metal part by immersion in a tank including pretreatment systems for preparing a metal part such as an automotive body for paint application.
Pretreatment refers to treatment of a metal surface such as an automobile body in preparation for subsequent electrodeposition paint application via an electrocoat tank. A typical vehicle body arrives at a pretreatment apparatus covered with metal-forming oils, grinding dust and other environmental contaminants. Each of these must be removed in order to apply a defect-free phosphate coating. Pretreatment includes a series of surface cleaning stages followed by phosphating, or the application of another conversion coating. Zinc phosphate is the principal conversion coating used in the automobile industry today, although iron phosphate is widely used in other applications. The pretreatment process includes a series of steps designed to remove contaminants from the metal surface, convert the surface to an inorganic crystalline coating, and seal the crystalline structure.
One example of an immersion zinc phosphating system includes nine stages: spray cleaner, immersion cleaner, spray rinse, immersion conditioner rinse, immersion zinc phosphate, immersion rinse, immersion chromic acid rinse, immersion recirculated deionized water rinse, and spray virgin deionized water rinse. The first two stages, the spray cleaner and immersion cleaner stages, clean the surface of contaminants to prepare the surface to form a tight, adherent, fine-grained zinc phosphate coating. Absent a clean surface, the first layer of paint, commonly referred to as an electrodeposition coating, will not adhere properly resulting in paint defects projecting through the topcoat or premature corrosion. The third stage, the spray rinse stage, follows cleaning and rinses the cleaning solution from the metal surface. Failure to rinse the cleaning solution results in contamination of subsequent chemical treatment stages. The immersion conditioner rinse stage, stage four, increases nucleation sites on the metal surface, thereby reducing the amount of zinc phosphate required to coat the surface and improving conversion coating uniformity. The immersion zinc phosphate stage, stage five, applies phosphate crystals to the metal surface, giving the surface corrosion-inhibiting properties and providing an improved base for paint application. Stage six, the immersion rinse, rids the surface of by-products from the zinc phosphate stage that could contaminate stage seven, the immersion chromic acid rinse. The chromic acid rinse removes remaining water soluble compounds from the surface to maximize corrosion protection. While the chromic acid rinse stage is not essential to the phosphating process, corrosion resistance of many substrates has proven to be greatly enhanced by the use of chromic acid. The last two stages, the recirculated deionized water rinse and the spray virgin deionized water rinse, remove all phosphate residue from the surface so as not to contaminate the electrocoat tank.
Each of the six immersion stages and the subsequent electrocoat process uses a tank having, for example, an 80,000 gallon capacity containing the various solutions required to complete the pretreatment process. As the metal surface enters and leaves each solution, spray nozzles positioned at an inlet and an outlet location above the immersion tank deluge the surface with the immersion solution. These spray nozzles frequently become clogged throughout the process. In the cleaning stages, contaminants from the metal surface, such as free carbon remaining on the surface from production grinding, clog the nozzles. In subsequent stages, the phosphating process causes chemical reactions creating by-products which clog the nozzles. For example, the immersion zinc phosphate stage creates an excess of iron phosphate, a white powdery substance coats the spray nozzles at the inlet and the outlet of the stage impeding the spray pattern needed to produce a satisfactory phosphate coating. Preferably, the spray nozzles are located above the immersion tanks just prior to the location where the vehicle bodies enter or leave the tank. To clean these spray nozzles, the immersion tank must be drained and scaffolding constructed above the tank to provide access to the nozzles, which is costly and time consuming.
It is therefore an object of the present invention to provide a spray nozzle apparatus which may be cleaned in a more efficient and less costly manner so that the time required to clean the nozzles can be reduced.
As set forth above, this invention relates to an apparatus for chemically treating a metal part particularly including phosphate or other conversion coatings via a pretreatment system including an immersion tank. The immersion tank contains a liquid chemical treatment solution including, but not limited to spray cleaner, immersion cleaner, spray rinse, immersion conditioner rinse, immersion zinc phosphate, immersion rinse, immersion chromic acid rinse, immersion recirculated deionized water rinse and spray virgin deionized water rinse as set forth above. The apparatus includes a conveyor conveying a metal part to be treated, such as an automotive body, from a first position above the immersion tank, then immersing the metal part in the liquid chemical treatment solution, and then removing the metal part from the immersion tank to a second position above the immersion tank. As will be understood, the first and second positions are generally adjacent opposed ends or end walls of the immersion tank, but the first and second positions may also be the same position or nearly the same, wherein the conveyor moves the metal part above the immersion tank, lowers the metal part into the liquid chemical treatment solution, raises the metal part and conveys the metal part away from the immersion tank.
The apparatus for chemically treating a metal part further includes at least one spray nozzle assembly located above the immersion tank which includes a plurality of spray nozzles spraying the metal part with the chemical treatment solution contained within the immersion tank. As set forth above, the spray nozzles frequently become clogged throughout the process requiring immediate or routine maintenance. In the apparatus for chemically treating a metal part of this invention, however, the spray nozzle assembly is supported on a track extending to at least a side wall of the immersion tank and is movable on the track to the side wall for periodic maintenance. In a preferred embodiment, the track extends beyond the adjacent side wall for maintenance outside the perimeter of the immersion tank. The spray nozzle assembly is conventionally connected to a header which may be located in the immersion tank, for example, or the header may be connected to a separate source of liquid chemical treatment solution. However, because the liquid chemical treatment solution drains from the part into the immersion tank, the liquid chemical treatment solution must generally be the same as the liquid chemical treatment solution in the immersion tank. Further, because the chemical treatment solution may attack or clog a conventional ferrous metal pipe, the pipes are generally stainless steel. Thus, provision must be made for disconnecting the lines from the header to the spray nozzle assembly. In the disclosed embodiment of the invention, the spray nozzle assembly is removably coupled to the header by conventional couplings. However, quick connect couplings may also be utilized or the spray nozzle assembly may be connected to the header by flexible hoses where the application permits.
In a preferred embodiment of the apparatus for chemically treating a metal part of this invention, the apparatus includes at least two spray nozzle assemblies including a first nozzle assembly located above the tank adjacent the first or inlet position of the part including a plurality of spray nozzles spraying the liquid chemical treatment solution onto the metal part prior to immersion of the part in the immersion tank including a first track extending to the first adjacent side of the immersion tank and movable on the first track to at least adjacent the first side of the tank and a second spray nozzle assembly located above the tank adjacent the second or outlet position also including a plurality of spray nozzles spraying liquid chemical treatment solution on the metal part in the second position supported on a second track extending to a second side wall of the immersion tank and movable to the second side wall for maintenance. In the disclosed embodiment, each of the first and second spray nozzle assemblies include an overhead spray assembly having a plurality of spray nozzles spraying the chemical treatment solution downwardly over the metal part and a side spray nozzle assembly or assemblies including a plurality of spray nozzles spraying the liquid chemical treatment solution laterally onto the part, and wherein each of the upper and side spray nozzle assemblies are independently supported on a track and movable to a side wall of the immersion tank as described above.
Thus, the apparatus for chemically treating a metal part of this invention significantly reduces the maintenance required for a treatment apparatus of this type disclosed including draining of the immersion tank for maintenance of the spray nozzle assemblies thereby significantly reducing the maintenance cost. Other advantages and meritorious features of the apparatus of this invention will be more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.